Welcome to the site!
Is the sucking loach a Hillstream loach? (pic:
http://www.aquarticles.com/images/Go...astromyzon.jpg) I know they are called several things, but just wanted to make sure I knew what you were talking about.
These are coolwater fish that like fast moving water. Do you have alot of water movement in the tank?
You have quite a load for a 10g tank. Do you have a test kit? If so, have you been keeping an eye on the ammonia, nitrite, and nitrate levels?
I know the Hillstream loaches (assuming that is what you have) like to eat microorganisms, so I'm wondering if its just eating stuff at the surface. I'm not certain though. The behavior seems a little strange for a Hillstream loach, but I've never kept one so I really don't know whats normal for them.
I'd check the ammonia, nitrite, and nitrates and make sure you have some water movement for the little guy. Also, what is the water temperature in the tank?
Have you asked the friend if the loach has been doing this previously?
If its not a hillstream loach, then could it be a Chinese Algae eater (
http://www.aquariumlife.net/profile-...lgae-eater.jpg)? If so, these usually stay near the bottom, so I'd say the behavior is a little strange. I'd still check the water parameters and see if something is off.